It is well known to measure voltages, such as differential voltages, having a common mode component. Further, it is known to measure a range of differential voltage using an integrated circuit. Where that range of measured voltage is above the capability or input range of the integrated circuit, it has been known to use a resistor bridge using external resistive components to provide a lower voltage representing that differential voltage within the operating range of the integrated circuit. That representation, a fraction of the voltage to be measured, is then applied to the IC and a signal representative of that measured voltage is obtained.
A problem raised by this known method of measurement outside the range of an IC is the requirement for a resistor bridge using components exterior to the IC. Reduction of the components by inclusion of at least some of the bridge resistors on the IC compromises the measurement. This follows as the ratio of resistors outside the IC to those resistors inside the IC cannot be maintained with consistent accuracy required for the voltage division. This is due to the variation between a) the resistors built on IC's, due to processing and during operation, and b) the resistors external to the IC.